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The Universe is believed to be between 10 and 20 billion years old! 1 EARTH • THIRD TERRESTRIAL PLANET FROM THE SUN • DIAMETER 12,756 KM • 1 A.U. (152,000,000 KM ) FROM SUN • EARTH 2 ASTRONOMICAL UNIT • AVERAGE DISTANCE FROM EARTH TO THE SUN • A.U.=150,000,000 km • If the mean distance of Earth from the Sun is 1 AU ("Astronomical Unit"), then that of Venus is 0.723 AU, of Mercury 0.387 AU and that of Mars is 1.524 AU. 3 MOON • Earth Distance 356,000 to 407,000 km • Equatorial diameter 3476 km • MOON 4 SOLAR SYSTEM • THE SUN AND ALL THE OBJECTS THAT TRAVEL AROUND IT • SUN, PLANETS, MOONS, ASTEROIDS, COMETS • SOLAR SYSTEM 5 SOLAR SYSTEM 6 SUN 4.6 billion years old. • The Sun is a medium size star known as a yellow dwarf. • SUN 7 LIGHT YEAR • DISTANCE LIGHT TRAVELS IN A YEAR • 63,000 A.U. • The Crab supernova remnant is about 4,000 light-years away. • The Milky Way Galaxy is about 150,000 lightyears across. • The Andromeda Galaxy is 2.3 million lightyears away. 8 PROXIMA CENTAURI Tiny Red Dwarf star some 4.22 lightyears away from us, third member of the Alpha Centauri triple system. 9 STAR CLUSTER • A GREAT MANY STARS CLUSTERED TOGETHER 10 GALAXY • STRUCTURE THAT CONTAINS HUNDREDS OF BILLIONS OF STARS • A cluster of stars, dust, and gas held together by gravity • TYPES OF GALAXIES 11 MILKY WAY GALAXY • 100,000 lightyears in diameter • SPIRAL GALAXY • 200 BILLION STARS 12 OUR MILKY WAY GALAXY 13 LOCAL GROUP • The Milky Way Galaxy belongs to the Local Group, a smaller group of 3 large and over 30 small galaxies 14 NEBULA • CLOUD OF DUST AND GAS IN WHICH NEW STARS ARE BORN 15 ROTATION • THE SPINNING MOTION OF A PLANET ABOUT ITS AXIS (DAY AND NIGHT) • The Earth rotates about an imaginary line that passes through the North and South poles of the planet. This line is called the axis of rotation. 16 REVOLUTION • THE MOVEMENT OF ONE OBJECT AROUND ANOTHER • EARTH’S REVOLUTION=1 YEAR • ALSO CALLED PLANETS ORBIT 17